The present invention relates to a vehicular power steering system, and more specifically, to a vehicular power steering system having means for controlling the degree of power assistance.
Vehicular power steering systems make the steering light and reduce driver fatigue. However, it is desirable to reduce the degree of power assistance in accordance with the vehicle speed because the steering becomes unstable and dangerous if the steering is too light at high vehicle speeds. On the other hand, if the steering wheel is turned rapidly, more hydraulic fluid is demanded by a hydraulic cylinder actuator of the power steering system. Accordingly, a rapid steering wheel movement tends to cause a lack of fluid supply to the cylinder actuator, resulting in a dangerous abrupt change of the steering effort.